The broad, long-term objective of this proposal is to improve the prognosis of patients with coronary artery disease. We propose to use magnetic resonance imaging (MRI) to guide percutaneous transluminal angioplasty (PTA) of coronary arteries and to measure the effect of PTA on myocardial perfusion. MRI has several potential advantages over conventional x-ray guidance for coronary PTA. MRI does not require the use of iodinated contrast medium, which has risks of renal toxicity and allergic reaction. This advantage is especially important to patients with poor kidney function. MRI permits direct monitoring of changes in cardiac perfusion at the time of PTA, a capability that can lead to changes in the anticipated treatment and may predict the success of the therapy. Unlike x-ray, MRI does not require the use of ionizing radiation, which can harm the patient. Additionally, the operating physician and hospital staff can benefit greatly by avoiding the cumulative effects of a lifetime of ionizing radiation exposure. The specific aims of the project are to use phantoms and canine models to test the following hypotheses: Specific Aim 1: MRI can achieve the frame rate and spatial resolution for device tracking and roadmap acquisition for guiding coronary PTA. Specific Aim 2: Catheter-based diagnostic coronary MR angiography accurately depicts coronary artery stenoses. Specific Aim 3: The technical success rates for MRI- and x-ray-guided PTA of coronary artery stenoses in canines are similar. Specific Aim 4: Successful MRI-guided PTA of coronary artery stenoses improves myocardial perfusion as measured with MRI at the time of the procedure. Successful completion of the project will serve as the foundation for further technical improvements. After more experience is gained, we anticipate a shift towards MIRI guidance for coronary interventions because of its capability to perform accurate functional assessment at the time of the intervention.